"The 1000-year-old market has been gutted, and the rebel-controlled west lies in ruin," Foley wrote in the article, published a month before his abduction.

"Last week's massive suicide car bombings, which levelled blocks of the government centre, left craters some 10 feet deep."

His kidnapping was not the first time he had been detained while reporting on an international crisis.

In 2011, he was taken while covering the uprising against Libyan dictator Muammar Gaddafi. Gaddafi’s forces released him after six weeks in captivity.

Foley later returned to Libya to cover Gaddafi’s fall and eventual death.

Just two weeks after he was released in Libya, Foley returned to Northwestern University to speak to students about reporting from conflict zones.

He said at the time that he believed it was essential to get close to conflict to "understand the world".

"Feeling like you've survived something, you know, it's a strange sort of force that you are drawn back to. I think that's the absolute reality," he said during the speech, which has been posted on YouTube.

Sotloff, who appeared at the end of the video posted on Tuesday, went missing in northern Syria while reporting in July 2013. He has written for Time magazine, among other news organisations.